藏南江孜地区海相白垩系化学地层学
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摘要
化学地层学是近三十年兴起的学科,是地层学新的发展方向,对于地层学的发展起到推动作用,化学地层同样具有地层划分与对比等方面的意义。白垩纪在地质历史中是一个特殊的时期,在科学研究中占有重要地位,我国海相白垩系主要分布于特提斯喜马拉雅带,该带以定日—定结—岗巴断层为界分为南带和北带,南带以定日、岗巴地区为代表,北带以江孜地区为代表,本文以江孜地区床得剖面为代表,论述了其化学地层学特征以及不同层段地球化学变化规律。
前人对江孜地区海相白垩系做过一系列研究,由下而上可以分为五个岩石地层单元:黑层、白层、硅质岩段、红层和滑塌层。前人在地球化学研究基础上得出前三者为缺氧沉积,而红层形成于富氧环境。本次工作在此基础上,详细地记录了岩石的颜色特征,并系统地研究了床得剖面地球化学方面特性,对已有的数据进行了加密,使之达到一个较高的分辨率。更清晰地反映出从黑层、白层、硅质岩段及红层地球化学指标变化规律,并依据不同地球化学指标,以床得剖面为代表,对江孜地区海相白垩系进行了化学地层划分。具体工作主要包括TOC、CaCO_3、常量元素含量、漫反射光谱学特性,并分析了样品中铁氧化物组成,得出床得剖面白垩纪地层具有以下特征:
TOC含量具有明显的旋回性,从黑层至硅质岩段可划分出十次旋回,而红层由于TOC含量极低,不具有旋回性特征,在黑层顶部,TOC含量达到峰值。
CaCO_3含量以白层最高,黑层底部、硅质岩段及红层CaCO_3含量极低,整体而言,CaCO_3含量规律性不明显。
铁、铝、钾、磷、镁、铊等含量变化特征相似,黑层顶部出现一次骤升,在红层平均含量达到最高,而硅含量变化与此相反,锰含量低,变化不明显,钠、钙等含量有较大的变化幅度。
FeO含量与全铁含量变化曲线近负相关,造成在红层内Fe~(3+)/Fe比值显著升高。
沉积物可见光反射率与颜色密切相关,黑层和红层平均可见光反射率低,而白层和硅质岩段高,反射率也与铁含量相关。铁含量以及Fe~(3+)/Fe升高,对于黄、橙、红等波段反射率上升。同样,样品中漫反射光谱特与多个地球化学指标有关,钙含量高,平均
Cretaceous is a special period of many climatic and tectonic changes, therfore very important in geosciences research. Marine Cretaceous strata crops out in Tethyan Himalaya zone. The latter is divided into northern subzone of Tethyan Himalayas (northern subzone) and southern subzone of Tethyan Himalayas (southern subzone) by the Dingri-Dingjie-Gangba fault. Gyangze area is located in the northern subzone. In this paper, the geochemical characteristic of the Chuangde section located in the Gyangze area is discussed.Marine Cretaceous strata at Gyangze area have been studied by several geologists, who established that the Gybure Formation was deposited in dysoxic environment. In a contrast the Chuangde Formation formed during time period when the ocean bottom water was rich in dissolved oxygen. The geochemical characteristics of Chuangde section is analyzed with higher precission than was previously available and include total organic carbon (TOC), calcium carbonate (CaCO_3), main elements, Fe oxides and features of Diffuse Reflectance Spectrocopy.TOC data divide the sequence into ten cycles, from the black unit up to the siliceous unit. The red beds have lower TOC content. TOC is highest at the top of the black unit.CaCO_3 content reaches the peak in white unit. CaCO_3 is very low at the bottom of black unit, siliceous unit and in red beds.Fe, Al, K, P, Mg and Ti have a similar behavior through the section. They increase sharply at the top of black unit, and reach highest content in red bed. This trend is opposite to the changes in the Si content. Mn has a lower content than the above elements and does not show any obvious pattern. Na and Ca content show high variability through the section. Fe~2+ contents is lowest in red bed, but the Fe~3+ reaches the peak.The Diffuse Reflectance Spectrocopy was used to correlate reflectancy with the content of Ca, TOC, and Fe. Reflectancy is increasing with an increase in Ca content and decreasing
前人对江孜地区海相白垩系做过一系列研究,由下而上可以分为五个岩石地层单元:黑层、白层、硅质岩段、红层和滑塌层。前人在地球化学研究基础上得出前三者为缺氧沉积,而红层形成于富氧环境。本次工作在此基础上,详细地记录了岩石的颜色特征,并系统地研究了床得剖面地球化学方面特性,对已有的数据进行了加密,使之达到一个较高的分辨率。更清晰地反映出从黑层、白层、硅质岩段及红层地球化学指标变化规律,并依据不同地球化学指标,以床得剖面为代表,对江孜地区海相白垩系进行了化学地层划分。具体工作主要包括TOC、CaCO_3、常量元素含量、漫反射光谱学特性,并分析了样品中铁氧化物组成,得出床得剖面白垩纪地层具有以下特征:
TOC含量具有明显的旋回性,从黑层至硅质岩段可划分出十次旋回,而红层由于TOC含量极低,不具有旋回性特征,在黑层顶部,TOC含量达到峰值。
CaCO_3含量以白层最高,黑层底部、硅质岩段及红层CaCO_3含量极低,整体而言,CaCO_3含量规律性不明显。
铁、铝、钾、磷、镁、铊等含量变化特征相似,黑层顶部出现一次骤升,在红层平均含量达到最高,而硅含量变化与此相反,锰含量低,变化不明显,钠、钙等含量有较大的变化幅度。
FeO含量与全铁含量变化曲线近负相关,造成在红层内Fe~(3+)/Fe比值显著升高。
沉积物可见光反射率与颜色密切相关,黑层和红层平均可见光反射率低,而白层和硅质岩段高,反射率也与铁含量相关。铁含量以及Fe~(3+)/Fe升高,对于黄、橙、红等波段反射率上升。同样,样品中漫反射光谱特与多个地球化学指标有关,钙含量高,平均
Cretaceous is a special period of many climatic and tectonic changes, therfore very important in geosciences research. Marine Cretaceous strata crops out in Tethyan Himalaya zone. The latter is divided into northern subzone of Tethyan Himalayas (northern subzone) and southern subzone of Tethyan Himalayas (southern subzone) by the Dingri-Dingjie-Gangba fault. Gyangze area is located in the northern subzone. In this paper, the geochemical characteristic of the Chuangde section located in the Gyangze area is discussed.Marine Cretaceous strata at Gyangze area have been studied by several geologists, who established that the Gybure Formation was deposited in dysoxic environment. In a contrast the Chuangde Formation formed during time period when the ocean bottom water was rich in dissolved oxygen. The geochemical characteristics of Chuangde section is analyzed with higher precission than was previously available and include total organic carbon (TOC), calcium carbonate (CaCO_3), main elements, Fe oxides and features of Diffuse Reflectance Spectrocopy.TOC data divide the sequence into ten cycles, from the black unit up to the siliceous unit. The red beds have lower TOC content. TOC is highest at the top of the black unit.CaCO_3 content reaches the peak in white unit. CaCO_3 is very low at the bottom of black unit, siliceous unit and in red beds.Fe, Al, K, P, Mg and Ti have a similar behavior through the section. They increase sharply at the top of black unit, and reach highest content in red bed. This trend is opposite to the changes in the Si content. Mn has a lower content than the above elements and does not show any obvious pattern. Na and Ca content show high variability through the section. Fe~2+ contents is lowest in red bed, but the Fe~3+ reaches the peak.The Diffuse Reflectance Spectrocopy was used to correlate reflectancy with the content of Ca, TOC, and Fe. Reflectancy is increasing with an increase in Ca content and decreasing
引文
[1] 崔杰,王成善.藏南岗巴地区上白垩统海相碳酸盐岩碳稳定同位素研究.沉积与特提斯地质,2003,23(2):9～13
[2] 胡修棉.特提斯喜马拉雅晚白垩世富氧问题探讨:[学位论文].成都:成都理工大学,1998.
[3] 胡修棉.藏南白垩系沉积地质与上白垩统海相红层——大洋富氧事件:[学位论文].成都:成都理工大学,2002.
[4] 胡修棉,王成善,李祥辉等.西藏南部赛诺曼阶—土仑阶缺氧事件:有机地球化学研究.地球化学,2000,29(5):417～424.
[5] 胡育筑主编.分析化学简明教程.北京:科学出版社,2004.
[6] 李祥辉,王成善,崔杰.高分辨率碳氧同位素应用及西藏岗巴地区白垩纪中期赛诺曼阶—土仑阶期碳同位素偏移.地学前缘,2005,12(2):171～178.
[7] 李祥辉,王成善,万晓樵等.藏南江孜县床得剖面侏罗—白垩纪地层层序及地层划分.地层学杂志,1999,23(4):303～309.
[8] 马宗晋,杜品仁,卢苗安.地球的多圈层相互作用.地学前缘,2001,8:3～8.
[9] 陶然.西藏南部中白垩世古海洋学研究:[学位论文].成都:成都理工大学,1989.
[10] 王成善,李祥辉,万晓樵等.西藏南部江孜地区白垩系的厘定.地质学报,2000,74(2):97～107.
[11] 王义刚,王玉净,吴浩若.西藏南部加不拉组问题的讨论及隆子地区下侏罗统的发现.地质科学,1976,2:150～156.
[12] 魏玉帅,王成善.土耳其—高加索—喜马拉雅一线白垩纪大洋红层对比.地学前缘,2005,12(2):51～59.
[13] 吴浩若.西藏地层—特提斯喜马拉雅北部分区.北京:科学出版社,1984,
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[15] 吴浩若,李红生.藏南宗卓组滑塌堆积中的放射虫化石.古生物学报,1982,21(1):64～71.
[16] 吴浩若,王东安,王连城.西藏南部拉孜—江孜一带的白垩系.地质科学,1977,3:250～261.
[17] 西藏地质矿产局.西藏自治区岩石地层.武汉:中国地质大学出版社,1997.
[18] 徐钰林,万晓樵,苟宗海.西藏侏罗、白垩、第三纪生物地质.武汉:中国地质大学出版社,1989.
[19] 徐钰林,万晓樵,苟宗海等.西藏侏罗纪.白垩纪,第三纪地层.武汉:中国地质大学出版社,1990.
[20] 杨遵仪,吴顺宝.西藏南部晚侏罗世的若干箭石.古生物学报,1964,12(2):187～216.
[21] 余光明,兰伯龙,王成善.西藏江孜地区白垩纪深海中的滑塌堆积和浊流沉积作用.见:青藏高原地质文集(15).北京:地质出版社,1984,13～26.
[22] 余光明,王成善.西藏特提斯沉积地质.见:地质专报(三,12).北京:地质出版社,1990.
[23] Arthur M A, Dean W E, Pratt L M. Geochemical and climatic effects of increased marine organic carbon. Nature. 1987.315: 216～218.
[24] Arthur M A, Sageman B B. Marine black shales: depositional mechanisms and environments of ancient deposits. Annu. Rev. Earth planet. Sci., 1994. 22: 499～551.
[25] Bak K. Planktonic foraminiferal biostratigraphy, Upper Cretaceous red Pelagic deposits, Pieniny Klippen Belt, Carpathians. Studia Geologica Polonica, 1998, 111 (13): 7～92.
[26] Barrera E., and Johnson C. C., Evolution of the Cretaceous Ocean-Climate system. Boulder Colorado. Geological Society of America Special Paper, 1999, 332, 445p.
[27] Berner A R and Raiswell R. C/S method for distinguishing freshwater from marine sedimentary rocks. Geology. 1984, 12, 365～368.
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[29] Caus E, Teixell A, Bernaus J M. Depositional model of a Cenomanian-Turonian extensional basin(Sopeira Basin, NE Spain): interplay between tectonics, eustasy and biological productiveity. Palaeogeography Palaeoclimate Palaeoecology, 1997, 129: 23～36.
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[32] Gorur N, Tuysuz O, Aykol A, Sakinc M et al., Cretaceous red pelagic carbonates of northern Turkey; their place in the opening history of the Black Sea. Eclogae Geologicae Helvetiae, 86: 819～838
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[2] 胡修棉.特提斯喜马拉雅晚白垩世富氧问题探讨:[学位论文].成都:成都理工大学,1998.
[3] 胡修棉.藏南白垩系沉积地质与上白垩统海相红层——大洋富氧事件:[学位论文].成都:成都理工大学,2002.
[4] 胡修棉,王成善,李祥辉等.西藏南部赛诺曼阶—土仑阶缺氧事件:有机地球化学研究.地球化学,2000,29(5):417～424.
[5] 胡育筑主编.分析化学简明教程.北京:科学出版社,2004.
[6] 李祥辉,王成善,崔杰.高分辨率碳氧同位素应用及西藏岗巴地区白垩纪中期赛诺曼阶—土仑阶期碳同位素偏移.地学前缘,2005,12(2):171～178.
[7] 李祥辉,王成善,万晓樵等.藏南江孜县床得剖面侏罗—白垩纪地层层序及地层划分.地层学杂志,1999,23(4):303～309.
[8] 马宗晋,杜品仁,卢苗安.地球的多圈层相互作用.地学前缘,2001,8:3～8.
[9] 陶然.西藏南部中白垩世古海洋学研究:[学位论文].成都:成都理工大学,1989.
[10] 王成善,李祥辉,万晓樵等.西藏南部江孜地区白垩系的厘定.地质学报,2000,74(2):97～107.
[11] 王义刚,王玉净,吴浩若.西藏南部加不拉组问题的讨论及隆子地区下侏罗统的发现.地质科学,1976,2:150～156.
[12] 魏玉帅,王成善.土耳其—高加索—喜马拉雅一线白垩纪大洋红层对比.地学前缘,2005,12(2):51～59.
[13] 吴浩若.西藏地层—特提斯喜马拉雅北部分区.北京:科学出版社,1984,
[14] 吴浩若.西藏南部江孜地区晚白垩世晚期及早第三纪地层?.地层学杂志,1987,11(2):147～149.
[15] 吴浩若,李红生.藏南宗卓组滑塌堆积中的放射虫化石.古生物学报,1982,21(1):64～71.
[16] 吴浩若,王东安,王连城.西藏南部拉孜—江孜一带的白垩系.地质科学,1977,3:250～261.
[17] 西藏地质矿产局.西藏自治区岩石地层.武汉:中国地质大学出版社,1997.
[18] 徐钰林,万晓樵,苟宗海.西藏侏罗、白垩、第三纪生物地质.武汉:中国地质大学出版社,1989.
[19] 徐钰林,万晓樵,苟宗海等.西藏侏罗纪.白垩纪,第三纪地层.武汉:中国地质大学出版社,1990.
[20] 杨遵仪,吴顺宝.西藏南部晚侏罗世的若干箭石.古生物学报,1964,12(2):187～216.
[21] 余光明,兰伯龙,王成善.西藏江孜地区白垩纪深海中的滑塌堆积和浊流沉积作用.见:青藏高原地质文集(15).北京:地质出版社,1984,13～26.
[22] 余光明,王成善.西藏特提斯沉积地质.见:地质专报(三,12).北京:地质出版社,1990.
[23] Arthur M A, Dean W E, Pratt L M. Geochemical and climatic effects of increased marine organic carbon. Nature. 1987.315: 216～218.
[24] Arthur M A, Sageman B B. Marine black shales: depositional mechanisms and environments of ancient deposits. Annu. Rev. Earth planet. Sci., 1994. 22: 499～551.
[25] Bak K. Planktonic foraminiferal biostratigraphy, Upper Cretaceous red Pelagic deposits, Pieniny Klippen Belt, Carpathians. Studia Geologica Polonica, 1998, 111 (13): 7～92.
[26] Barrera E., and Johnson C. C., Evolution of the Cretaceous Ocean-Climate system. Boulder Colorado. Geological Society of America Special Paper, 1999, 332, 445p.
[27] Berner A R and Raiswell R. C/S method for distinguishing freshwater from marine sedimentary rocks. Geology. 1984, 12, 365～368.
[28] C. S. Wang, X. M. Hu, L. Jansa et al., The Cenomanian-Turonian anoxic event in southern Tibet. Cretaceous Research, 2001, 22: 481～490
[29] Caus E, Teixell A, Bernaus J M. Depositional model of a Cenomanian-Turonian extensional basin(Sopeira Basin, NE Spain): interplay between tectonics, eustasy and biological productiveity. Palaeogeography Palaeoclimate Palaeoecology, 1997, 129: 23～36.
[30] Farrimond P, Eglinton G, Brassell S C, et al., The Cenomanian-Turonian anoxic event in Europe: An organic geochemical study. Mar Petrol. Geol., 1990, 7: 75～89.
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